The present invention relates to a device and a method for regulating the lift characteristic of a charge cycle valve of an internal combustion engine.
In traditional combustion engines, the camshaft is driven mechanically by the crankshaft via a control chain or a control belt. To increase engine power and reduce fuel consumption, it is very advantageous to control the valves of the individual cylinders individually. This is possible through a so-called fully variable valve drive (variable control times and variable valve lift), e.g., a so-called electromagnetic valve drive. With a fully variable valve drive, an “actuator unit” is allocated to each valve and/or each “valve group” of a cylinder. At the present point in time, different basic types of actuator units are being researched.
With one basic type (so-called lift actuators), an opening magnet and a closing magnet are allocated to a valve or a valve group. The valves may be displaced axially, i.e., opened and/or closed, by supplying the magnets with electric power.
With another basic type (so-called rotary actuator) a control shaft is provided with a cam, whereby the control shaft is pivotable back and forth by an electric motor.
German Patent Document DE 101 40 461 A1 describes a rotary actuator device for controlling the lift of a charge cycle valve. The lift is controlled here by an electric motor, which is itself controlled by an engine characteristics map, a shaft with a control cam connected to it in a rotationally fixed manner being arranged on the rotor of said electric motor. During operation of the internal combustion engine, the motor pivots, i.e., swings back and forth, and the control cam periodically forces the charge cycle valve into its open position via a roller-lever actuator. The charge cycle valve is closed by the spring force of a valve spring. In order for the electric motor not to have to overcome the total spring force of the valve spring in opening the charge cycle valve, an additional spring is mounted on the shaft. The forces of the valve spring and additional spring are such that in periodic operation of the rotational actuator device according to the position of the charge cycle valve, the kinetic energy is either stored in the valve spring or in the additional spring. As a result of this measure, the power consumption during operation of the rotary actuator device is reduced. One disadvantage of the rotary actuator device described here is the high power consumption at low rotational speeds.
German Patent Document DE 102 52 991 A1 describes a further embodiment of such a rotary actuator device. The existing rotary actuator device is expanded here by a second actuator element (second control cam) in the opposite direction of rotation and with a smaller lift than that of the main cam. This second actuator element does not open the valve completely and is used only for small lifts in the range of low engine rotational speeds. At low rotational speeds of the internal combustion engine, the rotary actuator device receives electric power, so that the shaft pivots only in the direction of the second actuator element, whereas at high rotational speeds, the motor is swiveled only in the direction of the first actuator element. Due to the small lift, the rotary actuator device advantageously consumes less electric current at a low rotational speed.
The object of the present invention is to create a device for regulating the lift characteristic of a charge cycle valve that ensures an improvement with regard to electric power consumption by an actuator device.
According to this invention, this object is achieved by the totality of features of the independent claims.
The inventive device for regulating the lift characteristic of a charge cycle valve comprises a regulating device (so-called setpoint path regulator) which controls a drive unit (e.g., the electric motor of a rotary actuator or the electromagnet(s) of an electromagnetic lift actuator or the drive mechanism of a slewing actuator) according to a stored setpoint path, whereby the setpoint path is such that it maps the ideal transient characteristic of the energy storage-drive element-energy storage system (spring-mass-spring system) of the actuator device (plus the valve unit to be driven with the charge cycle valve and the closing spring). Stored setpoint path(s) in the sense of this invention include setpoint paths (data) stored once in a memory as well as stored calculation procedures on the basis of which such a setpoint path can be calculated online. This device is to be used to advantage in a rotary actuator device according to German Patent Document DE 101 40 461 A1, where it should reduce the power consumption of the electric motor used here by regulating the rotational characteristic of the rotor of the drive motor according to the ideal setpoint path of the oscillating system of the rotary actuator device as determined here. On the basis of this regulation, a regulating behavior is then established, in which the electric motor smoothes out ambient influence such as friction and gas backpressure that deviate from the ideal (calculated) oscillating system by supplying additional driving power.
An ideal transient characteristic in the sense of this invention is characterized in that the oscillating behavior is free of friction losses and ambient influences such as gas pressures and gas backpressures. Ideally, an ideal oscillating behavior corresponds to the calculated oscillating characteristic of the system, free of any type of losses. The present invention advantageously relates to a spring-mass-spring system (according to German Patent Document DE 101 40 461 A1) having a valve restoring spring and/or opening spring (spring 1), an opening spring (spring 2) that counteracts the valve restoring spring and the mass moving between the springs in this system (e.g., rocker lever, drive cam plus driveshaft and rotor of the driven electric motor, mass components of the opening spring acting on the drive cam in the opening direction as well as the charge cycle valve plus amounts by weight of the moving closing spring).
In a particularly preferred refinement of the present invention, the device includes a rotary actuator device according to German Patent Document DE 103 58 936 which was not published previously. DE 103 58 936 is herewith incorporated with its full content in the disclosure of the present patent application in particular with regard to the design of a rotary actuator (but here in particular with regard to the arrangement and design of the opening spring as a rotary rod spring).
In another refinement of this invention, the rotary actuator is designed according to German Patent Document DE 102 52 991 A1 with an actuating element in the form of a so-called double cam driven by an electric motor. With regard to the special embodiment of a double cam having two such control paths, the content of German Patent Document DE 102 52 991 A1 is herewith also incorporated in the disclosure content of the present patent application.
To further reduce the energy demand by a rotary actuator, a plurality of so-called ideal setpoint paths are stored, each setpoint path describing a different valve lift. In one embodiment, at least one setpoint path with a maximum lift and one setpoint path with a reduced lift by comparison are stored as fixed setpoint paths (stored trajectory or corresponding calculation procedure). In a refinement, any curve characteristics required between these at least two fixed setpoint paths are formed by interpolation between the stored setpoint paths. Further refinements of the present invention relate to the design of the actuator device as a rotary actuator according to German Patent Document DE 101 40 461 A1 and according to German Patent Document DE 103 58 936.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.